Biomedical Engineering Reference
In-Depth Information
(A)
(B)
Polymer swelling
Nanometer-level profiling
80
60
30
Water
47 nm
20
∼
20 nm
∼
55 nm
40
10
0
9
20
18
17
10
11
16
12
15
13
14
14
13
15
12
y
(
μ
m)
x
(
μ
m)
0
0.2
0.4
0.6
0
0.8
y
(mm)
Figure 18.8
(A) Single QD localization measurements before (dark gray) and after swelling (light gray) of a six-
bilayer polymeric substrate. Adding water resulted in an increase of the substrate thickness by
20
5 nm. No lateral shifts of QDs were observed across a large field of view. (B) Nanometer-
level profiling of a transparent nano-etched surface by SD-FPM. Source: (A) This figure is reproduced
from figure 5(a) of Ref.
[42]
with permission of the Optical Society of America. (B) This figure is reproduced
from figure 6(b) of Ref.
[40]
with permission of John Wiley & Sons Ltd.
6
In a different experiment, we measured the thickness of a calibrated sample by using the
SD-FPM system shown in
Figure 18.3A [39,40]
. The sample comprised a step pattern
etched on one surface of a coverslip where fluorescent beads were dried on the second
surface. The step profile was obtained by computing the differential spatial phase of
excited fluorophores along a single axial cross-section of the sample as expressed by
z
j
(x,y)
2,
I
peak
(x
5
x
0
, y
5
y
0
), where z
j
(x,y) represents the axial displacement
at a given transversal coordinate (x,y) and (x
0
,y
0
) is a reference coordinate. The surface
profile was obtained by averaging several consecutive profiles (each recorded in a single
shot) to increase the measurement accuracy. As shown in
Figure 18.8B
, this measurement
predicts a step profile with a thickness (depth) of
B
55 nm which is comparable to the
47 nm thickness measured independently by SD phase microscopy
[26]
.
~,
I
peak
(x,y)
18.5 Conclusions and Outlook
The phase of fluorescent light waves is largely unexplored in the development of new tools
of fluorescence microscopy. However, it comprises a novel source of information about the
wave and can be used to yield new forms of optical imaging technologies with nanoscopic
and mesoscopic resolution scales. In this chapter, we presented two new methods that
employ concepts of white-light interferometry to retrieve this phase information and
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